1. Field of the Invention
The present invention relates to a slide member and, more particularly, to a slide member suitable for use in an element having a surface on which a magnetic recording medium such as a magnetic tape travels, such as a head drum assembly or a tape guide member for a video tape recorder.
2. Brief Description of the Prior Art
A material which has heretofore been employed for a slide member such as a stationary drum or a rotary drum for the head drum assembly of a video tape recorder or the like is AC8A, AC8B or AC5A of the Al-Si-Cu-Ni-Mg alloy type or the like and the sliding surface of the slide member is planished or finished so as to give a degree of surface roughness of about 1 to 3 microns on the drum surface or the tape guide surface. Where AC8A or AC8B is employed for the sliding surface of the slide member on which a magnetic tape travels, it is composed of an aluminum solid solution or a eutectic alloy and a coefficient of friction (.mu.) on the sliding surface thereof is in the scope ranging from about 0.25 to 0.3 so that is has a longer life than AC5A. With the sliding surface composed of AC8A or AC8B, however, that portion is so soft that the surface condition such as a degree of surface roughness on the drum surface is impaired and the coefficient of friction is changed when it is operated for a long period of time. These may cause the magnetic tape to stick to the surface of the drum, whereby noises are caused to occur. In worst cases, the magnetic tape is caused to stick to the surface of a tape guide portion and to become inoperable. These are extremely unfavorable for the operation of apparatus equipped with a slide member. In instances where the surface of the tape guide portion is worn away, an extremely high precision required for positioning the magnetic tape is encountered, whereby serious problems are caused in operation. The wear of the tape guide portion or surface may cause a deviation or divergence of the traveling tape from the normal position and leads to an aberration in a state of contact of the tape edge with the tape lead of the drum so that problems with the rubbing-off of magnetic powders are encountered. Magnetic powders rubbed off from the magnetic layer of the magnetic tape may damage the slide or tape guide surface of a slide member.
The addition of Si to such materials can generally decrease the coefficient of friction. The Si content in AC5A, however, is insufficient so that it cannot permit a satisfactory effect desired by the addition of Si. In instances where materials having a lesser Si content are used for the slide member, the sliding surface tends to wear away causing an increase in the coefficient of friction. Even AC8A and AC8B which each contain a Si content greater than AC5A are insufficient in conditions under which the magnetic tape traveling on the slide member is in touch with the sliding surface thereof. It is also proposed that a beta phase having a eutectic structure between Al and Si as a major component be employed as a drum material for the peripheral drum surface portion. This drum material has a coefficient of friction of 0.22 to 0.24 when finished into a planished surface and this coefficient is somewhat lower than that of a general aluminum alloy.
Conventional materials used for the slide member usually have a too high coefficient of thermal expansion. They accordingly have some difficulty in maintaining initial conditions such as a bearing pilot pressure.
The slide member applied to the drum assembly of a video tape recorder contains a range where the Reynolds number is large and the area should be maintained in a spatial relationship from the traveling magnetic tape; otherwise, the traveling magnetic tape may be caused to stick to the surface of the drum assembly, causing noises to occur during operation of the video tape recorder. Although the slide member to be used for this purpose may preferably have a degree of surface roughness ranging from approximately 0.2 to 0.5 micron on the tape guide or sliding surface thereof, slide members composed of conventional materials fail to permit a satisfactory degree of surface roughness in association with other conditions required for drum assemblies.